1. Field of the Invention
The present invention relates to high intensity focused ultrasonic technology, and particularly to a method for automatically selecting a region of interest for an MRI-guided high intensity focused ultrasonic system.
2. Description of the Prior Art
High Intensity Focused Ultrasonic (HIFU) is a method for curing tumors using the heating effects of ultrasonic waves that takes advantage of the excellent directivity and focusing capability of ultrasonic waves to focus low energy and low frequency ultrasonic waves outside a human body to a certain target area within (with a diameter usually less than 1 mm), and to utilize the bio-effects of the ultrasonic waves to instantaneously bring the temperature at the focus to above 65° C., which is the temperature for necrotizing cells, and to cause tissue's coagulative necrosis within said target area without damaging the surrounding normal tissues, thereby ablating the tumor non-intrusively. In addition, ultrasonic waves are not radioactive, therefore they can be used for treating a patient repeatedly, and this has become the new method of best potential developed over past few years for treating tumors.
Proton Resonance Frequency (PRF) shift thermometry is a high intensity focused ultrasonic method used under the guidance of magnetic resonance. In this method, a region of interest (ROI for short) covering the heated area is selected around the focused heated area. In the prior art, normally the region of interest is inferred and selected according to temperature variation, however, the selection is done manually instead of automatically. The technique of manually selecting the ROI has the following disadvantages:
1. Manual selection can not completely ensure that the entire heated area is included in the ROI;
2. If the selected region is too large, some unnecessary areas that should not be selected, such as a part of blood vessels and some unheated area will be included in the region of interest; and if the selected region of interest is too small, a part of the heated area will be excluded, which leads to a false result; and
3. The manual selection has poor reproducibility, the operation is time-consuming and the efficiency is low.